"Raquette" of course means "racket" or "snow shoe". Now, compare those to the shape of a frying pan, and you see why those names are given to dead-end streets or cul de sacs with a round end.

If you wish to remain as colloquial as the French you could call it the "turning frying-pan", otherwise "turning area" it will have to be.

turning area
Explanation:
I don't think there is a 'usual term' as such because it very much depends on the context. The generic term - which is quite well documented would be 'turning area' but it rather depends on which characteristic you are highlighting, since a Wendehammer is not only a turning area but also a cul-de-sac. If, for instance, it were simply a matter of giving directions ('Fahren Sie bis zum Wendehammer'), you would say, 'drive to the end of the road'. More context would help.
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That's what I'd use; colloquially, "frying-pan" is quite common, but it doesn't look as if you want it colloquially....
http://www.proz.com/kudoz/german_to_english/construction_civ...